Reactions among the following that occur during calcination are:

a. CaCO→ CaO + CO2
b. 2FeS2 + \(\frac{11}{2}\)O2 → Fe2O3 + SO2
c. Al2O3.xH2O → Al2O+ xH2O
d. ZnS + \(\frac{3}{2}\)O2 → ZnO + SO2

Choose the correct option:
1. a and b
2. b and c
3. c and d
4. a and c

HINT: Calcination = Absence of air or limited supply of air.
Explantion:
Calcination involves heating of the ore below its melting point in the absence of air or in limited supply of air. Oxygen containing ores like oxide, hydroxides and carbonates are calcined.
Thus, the following reactions occur during calcination.
CaCO3CaO + CO2Al2O3. xH2O Al2O3 +  xH2O